1. Field of the Invention
The present invention relates to a method and system for detection of, and compensation for, the rapid change in temperature on a pressure measurement cell. More specifically, the present invention relates to the detection and measurement of the temperature change by generating a measurement signal and a reference signal proportional to the deflection of a diaphragm and establishing a reference band therefrom.
2. Description of the Related Art
The related art involves the development and use of pressure measurement cells. Pressure measurement cells are known from EP 1186875 B1, for example. Such a pressure measurement cell usually consists of a base body and a measurement diaphragm, with a shallow recess provided on the base body, covered completely by the diaphragm which, together with the recess, forms a pressure chamber. Electrodes, which together form a measurement capacitor whose measurement signal is analyzed, are provided on the inside of the diaphragm and in the recess. To compensate for interference effects such as temperature or drift, a reference capacitor is set up next to the measurement capacitor.
If such a pressure measurement cell is in thermal equilibrium with its environment, the temperature dependence of the pressure measurement can be compensated by means of a temperature sensor installed on the back side of the base body. A rapid change in temperature, e.g., a so-called thermal shock, may lead to stresses in the diaphragm of the pressure measurement cell, resulting in incorrect measured values due to the resulting deflection of the measurement diaphragm. The stresses in the diaphragm result from a difference in temperature between a medium acting on the diaphragm of the pressure cell and the base body of the pressure measurement cell which carries the diaphragm and faces away from the medium but is thermally connected to the environment.
This problem is solved according to EP 1186875 B1 cited above by the fact that a second temperature sensor is set up in the direction of an expected temperature gradient, namely in a connecting layer between the diaphragm and the base body carrying this diaphragm. Changes in temperature with a steep temperature gradient can thus be detected rapidly, so that thermal shocks can be differentiated from an actual change in pressure and can be compensated.
What is not appreciated by the prior art is that one disadvantage of this known approach is that with larger measurement ranges (e.g., 60 bar), a change in temperature can be detected only with a time lag because of the thick diaphragm. However, changes in measurement signal due to thermal shock must take place very rapidly, so that error compensation by means of the two temperature sensors is highly inadequate, in particular when there is a large measurement range.
In addition, the production of such a pressure measurement cell according to EP 1186875 B1 is very complex and, therefore, also expensive, because introducing a temperature sensor into the joint area between the diaphragm and the base body of the pressure measurement cell as well as contacting it and analyzing the signal are associated with additional expense.
Accordingly, there is a need for an improved a method for detection of, and compensation for, the rapid change in temperature on a pressure measurement cell based on the finding that deformation of the diaphragm due to pressure differs significantly in terms of measurement technology in comparison with deformation of a diaphragm due to thermal shock.